<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        let num = 10 
        function fn1(){
            let num = 20
            function fn2(){
                let a = '20'
                function fn3(){
                    let num = 30
                    console.log(a)
                }
                fn3()
            }
            fn2()
        }
        fn1()
        console.log(num)
    </script>
</body>
</html>